Introduce MzContainerized, use in reachability logging

[antiguru]

Introduce a MzContainerized trait that associates types to regions, while allowing to specify a owned type that is different to Self. Switches reachability logging to send flat containers over dataflow edges. Changes mz_replay to accept a closure to produce data.

Related: #27741

Part of #13038

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• This PR includes the following user-facing behavior changes:

[frankmcsherry]

Looks good, with some comments about clarity and stumbling blocks I found.